This invention relates to a new and useful improvement in the preparation of isethionic acid.
The preparation of isethionic acid is known in the art. Sexton et al, (U.S. Pat. No. 2,810,747) teaches preparing isethionic acid from its alkaline salt from ethylene oxide and potassium or sodium bisulfite using high pressure equipment. Furthermore, Smith, (U.S. Pat. No. 2,899,461) primarily teahes that alkali metal salts of isethionic acid can be prepared by reacting at least an equimolar proportion of ethylene sulfite and an alkali metal carbonate or bicarbonate. Additionally, Smith discloses that free isethionic acid can be obtained from its alkaline metal salt by acidfication with a mineral acid.
Smith is an improvement over Sexton, and is regarded as the state of the art process. However, the Smith method has many problems and drawbacks. In one experiment employing the Smith method, isethionic acid was prepared by reacting sodium isethionate with an acidic ion exhange resin. First, it was observed that the ion exhange resins have a low capacity for reacting with sodium isethionate--about 2-10 milliequivalent/gm. Second, it was also observed that due to the difficulty of converting a weak basic compound, sodium isethionate, into a strong acidic compound, isethionic acid, the equillibrium of the reaction favors the sodium isethionate. As the sodium ions (Na.sup.+) displace hydrogen ions (H.sup.+) in the reaction zone some of the unreacted sodium isethionate will eventually "break through" out of the reaction zone. The reaction zone must therefore be periodically regenerated with hydrogen ion (H.sup.+) by the addition of a strong acid. One undesirable effect of this periodic reacidification procedure is that it leads to ion-exchange resin bead or particle breakage; which in turn results in an increase in the pressure drop across the reaction zone. Additionally, it results in an increase in downstream plugging. Third, this method is a very expensive method of preparing isethionic acid.
In view of the problems associated with the present state of the art, it is a desirable goal in the chemical industry to develop or discover a simple, improved and inexpensive process, that at a minimum, eliminates these problems and guarantees a better product yield.